We propose to isolate and completely characterize the erythropoiesis-specific histone H5 genes, as well as previously isolated embryonic and somatic (split) histone genes from our chicken genomic recombinant DNA library. Characterization will be by standard methodology (DNA sequencing, Southern and northern blotting, and electron microscopy). We will use the somatic histone gene as an in situ probe for localization of the coding sequence to a specific chicken macrochromosome. If embryonic, somatic and erythropoiesis-specific H5 genes are localized to a small region of a pure macrochromosome, isolation of linked H5 genes and other somatic genes will be effected by chromosome "walking". Using these isolated embryonic, somatic and erythropoiesis-specific genes, we plan to examine the effects of reintroduction of modified (methylated) gene copies into monkey cells (COS 1) using SV40 vectors to ask if site-specific methylation is sufficient for transcriptional shutdown. Using the same eucaryotic host/vector system, we plan to test the hypothesis that histone H5 is directly responsible for red cell transcriptional senescence. We plan parallel studies to examine the in vivo chromatin structure of embryonic and somatic genes in SV40-vector minichromosomes which contain histone gene copies and in developing chick tissue.